Microelectronic arrays having electronically addressable microlocations, or features, are being used to carry out in-parallel multiple sample DNA hybridization analysis on a source DNA sample. The microelectronic arrays are fabricated on semiconductor substrates using semiconductor processing techniques. An exemplary microelectronic array system for performing molecular biological diagnosis is disclosed in U.S. Pat. No. 5,632,957, entitled "Molecular Biological Diagnostic Systems Including Electrodes," issued to Heller et al. (hereinafter Heller). Microelectronic arrays such as Heller allow charged molecules to be actively moved and concentrated at designated microlocations within an array. In one application, DNA probes are located at specific microlocations and then target DNA molecules are electronically directed to specific probes in order to promote hybridization of the target DNA with the probe DNA. By utilizing electronically addressable microelectronic arrays to concentrate DNA, hybridization rates are significantly accelerated over prior passive hybridization techniques.
There are many techniques available for detecting the extent of DNA hybridization that has occurred on DNA arrays, whether microelectronic or not. A common technique involves incorporating fluorescent markers, or labels, into the target DNA that is provided to hybridize with the probe DNA. After hybridization, each microlocation can be contacted with light, for example laser light, in order to activate any fluorescent labels that are present at a particular microlocation. Fluorescent light given off from the fluorescent material located at the microlocations is measured and related to DNA concentrations.
In most detection techniques that require outside sources of energy, such as laser light energy, to activate a label, the activation energy is applied to the array one microlocation at a time. Specifically, in a laser-activated system, the laser systematically steps through each microlocation, or pixel, applying laser light to each location individually. Laser-based readout systems are disclosed in U.S. Pat. No. 5,631,734, entitled "Method and Apparatus for Detection of Fluorescently Labeled Materials," issued to Stern et al. and U.S. Pat. No. 5,653,939, entitled "Optical and Electrical Methods and Apparatus for Molecule Detection," issued to Hollis et al. Although sequentially reading out microlocations works well when the number of microlocations is small, when the number of microlocations in a microelectronic array is large, the readout time required to individually read each microlocation can be significant.
In view of the advancements involved with electrically addressable microelectronic arrays and in view of the limitations involved with sequentially activating microlocations on any DNA array with an outside source of energy such as laser light, what is needed is a readout method that takes advantage of the addressing control capability of microelectronic arrays in order to more efficiently read out desired biological data.